Persistent 2D photoconductivity and deep levels in AlxGa1-xAs/GaAs heterostructures

Abstract
AlGaAs/GaAs heterostructures exhibit a non-resonant oscillatory background signal in electron spin resonance (ESR) experiments which can be attributed to the Shubnikov-de Haas effect due to the two-dimensional electron gas. Illumination causes a persistent change both in oscillation period and the ESR of a new, probably Cr-related complex in GaAs. For the latter, the authors derive an energy level within 0.36 eV from the conduction band edge from photo-quenching and re-excitation. The photoexcitation rate for free carriers exhibits threshold energies of 0.7, 1.1 and 1.5 eV which they ascribe to the Cr photoexcitation (Cr2+ to Cr3++e-) in the substrate, the photoionisation of DX centres in the AlGaAs and interband excitation in GaAs respectively.